Multiple spool valve arrangements, frequently complicated and with special or custom components, have been provided for controlling multi-fluid supplies, including fuel and oxidant gases for fuel cells. Examples among U.S. patents are Knapp No. 4,087,967 (control for variable speed, reversible transmissions), Yoshino No. 3,554,213 (synchronization of pressured fluid flows for hydraulic devices), and Bauer No. 696,836 (control of variable speed reversible transmissions).